In my copending application Ser. No. 921,643 filed July 3, 1987 now Pat. No. 4,209,355 and titled MANUFACTURE OF BUMPED COMPOSITE TAPE FOR AUTOMATIC GANG BONDING OF SEMICONDUCTOR DEVICES a process is disclosed for creating an array of metal fingers that can be gang bonded to a semiconductor chip while still associated with a composite tape. This tape method of automatic assembly is capable of high speed so that assembly costs can be greatly reduced. After the semiconductor chip is bonded to the tape mounted fingers it can be automatically positioned with respect to the ultimate device mounting structure such as a lead frame or hybrid substrate. The chip and its bonded fingers can then be excised from the tape and gang bonded to the lead frame or hybrid substrate. Then conventional packaging is employed to complete the structure. As pointed out in the above-mentioned copending application, it is often desirable to create bumps on the metal fingers so that contact can be made to the conventional bonding pads normally employed on monolithic integrated circuit devices. Typically the fingers are made of copper which is thermocompression bonded, aluminum which is ultrasonically bonded, or tinned metal which is soldered. Ideally the plurality of bonds that must be made are completed simultaneously in what is called gang bonding. However, it has been found that gang bonding often results in a wide variability in individual bonds. This means that in a multiple bond operation the likelihood of at least one poor bond is high. This creates an intolerable reliability problem.
Soldering is regarded as useful, but the process must be kept extremely clean or corrosive fluxing must be used and solder flow must be controlled. Ultrasonic welding is effective but has not proven reliable in gang bonding and ultrasonic welding requires complicated equipment. Thermocompression bonding has worked out reasonably well, particularly on bumped semiconductor chips, but some problems are encountered, particularly in lead frame and hybrid substrate gang bonding.
One alternative that has been employed is wobble bonding. Here instead of trying to bond all fingers simultaneously, the bonding tool is tilted and rotated so that the bonding surface "walks" across the fingers in sequence. This is a compromise between gang bonding and single bonding and is very difficult to achieve in automatic equipment. At best it is slower than gang bonding.